Fabrication of magnetoresistive random-access memory (MRAM) devices normally involves a sequence of processing steps during which many layers of metals and dielectrics are deposited and then patterned to form a magnetoresistive stack as well as electrodes for electrical connections. To define those millions of MTJ cells in each MRAM device and make them non-interacting to each other, precise patterning steps including reactive ion etching (RIE) are usually involved. During RIE, high energy ions remove materials vertically in those areas not masked by photoresist, separating one MTJ cell from another. However, the high energy ions can also react with the non-removed materials, oxygen, moisture and other chemicals laterally, causing sidewall damage and lowering device performance.
To solve this issue, pure physical etching techniques such as ion beam etching (IBE) have been applied to etch the MTJ stack to avoid the damaged MTJ sidewall. However, due to their non-volatile nature, IBE etched conductive materials in MTJ and the bottom electrode can be re-deposited into the tunnel barrier, resulting in shorted devices. A new device structure and associated process flow which can form MTJ patterns with desired sizes without plasma etch is desired.
Several patents teach methods of forming an MTJ without etching, including U.S. Pat. No. 9,773,978 (Fraczak et al) and U.S. Patent Application 2017/0110649 (Diaz et al), but these methods are different from the present disclosure.